The detailed catalytic oxidation mechanisms of CO over Cr-embedded graphene have been investigated by means of M06-2X density functional. Both models with chromium atom embedded in single and double vacancy (Cr-SV and Cr-DV) in a graphene sheet were considered. It is found that the CO oxidation on Cr-SV-graphene prefers to Langmuir-Hinshelwood (LH) mechanism, while the Cr-DV-graphene shows good catalytic activity toward the CO oxidation via the Eley-Rideal (ER) mechanism. The present results imply that the low-cost Cr-embedded graphene is a prospective catalyst for CO oxidation at room temperature.